Animal Biology - GRE Subject Test: Biology

Antibodies are part of the adaptive immune response, which means that they are formed later in an infection. Because both recognition sites have the same structure, they are responsive to only one type of antigen. They are located on the outside of B cells, and can be released freely into the plasma by plasma cells.

Placental crossing is done mainly by IgG antibodies. These fast-acting antibodies provide temporary immunity for the fetus until it is able to have its own immune system produce sufficient antibody amounts.

The oropharynx is capable of accepting both air and food from the mouth and nose. In the laryngopharynx, however, a crucial division occurs. Food, solids, and liquids are passed down the esophagus, while air travels through the trachea to the lungs. During swallowing, the entrance to the trachea, the larynx, must be covered so that food does not go through the trachea and enter the lungs. This is accomplished by the epiglottis, an elastic cartilage structure that covers the larynx during swallowing.

While it is true that the liver creates and secretes bile, storage of bile is accomplished by the gall bladder.

Spinal nerves coming off of the spinal cord can be thought of as the combination of both posterior and anterior roots. This means that they contain both sensory and motor neuron axons. These nerves can also carry autonomic functions to organs of the body as well.

Cortisol is secreted by the adrenal gland. We need to identify the hormone responsible for stimulating the adrenal gland and prompting it to release cortisol. This job is accomplished by adrenocorticotropic hormone (or ACTH). While aldosterone is secreted by the adrenal gland, it does not impact the release of cortisol to any significant degree.

The two main hormones of interest that are secreted by the posterior pituitary gland are antidiuretic hormone (ADH) and oxytocin. Antidiuretic hormone plays a key role in retaining water at the level of the kidney. In patients with no ADH, fluid retention is severely diminished. Symptoms of this include frequent urination, hyperosmolality, and dehydration.

An antibody is very specific and will only attach to one antigen. Once it does, the antibody can signal the pathogen or infected cell to be destroyed by macrophages and other phagocytic cells in the body, such as cytotoxic T-cells. The antibodies themselves cannot destroy the pathogen.

T-cells serve important functions in the communication and stimulation of antibody production, but do not actually produce antibodies.

Antibodies are produced by the adaptive immune system and to antigens presented by a pathogen. The antibody-antigen complex is then detected by cytotoxic T-cells, which destroy the infected cell. The antibodies are created by B-lymphocytes, which can differentiate when exposed to a specific pathogen. Differentiated B-lymphocytes known as plasma cells are responsible for the mass production of certain antibodies.

Macrophages are derived from monocytes and serve as phagocytes in the innate immune response. Basophils are also part of the innate immune response and, along with mast cells, produce histamine to initiate the inflammatory response.

Acquired immunity is developed in the body following a previously encountered infection. The innate immunity is, by definition, always present in the body and is used to attack all general forms of infection.

The granulocyte cells are considered part of innate immunity and help mediate the immune response against foreign pathogens. These cells include basophils, neutrophils, eosinophils, mast cells, and macrophages (which are differentiated from monocytes).

The adaptive immune response involves the production of antibodies against specific target antigens. Plasma cells are an integral part of the adaptive response and secrete large volumes of antibodies in response to a secondary infection by a previously encountered pathogen. T-cells and B-cells are also part of the adaptive response.

The five types of leukocytes are: neutrophils, lymphocytes, monocytes, eosinophils, and basophils. Three of these (neutrophils, eosinophils, and basophils) contain granules, tiny sacs containing enzymes which can lyse microorganisms. The other two leukocytes (lymphocytes and monocytes) do not contain these granules.

There are many types of white blood cells with distinct functions in the body. Neutrophils and monocytes are phagocytes that engulf bacteria. B-lymphocytes produce one type of antibody. Basophils are the least common of the leukocytes, and release histamine during inflammation.

Before a B-lymphocyte can proliferate and differentiate, it must present its antigen to a helper T-cell. If the helper T-cell recognizes the antigen as foreign, it will activate the B-lymphocytes, and cause them to differentiate into plasma cells and memory B-cells.

T and B cells are both part of the adaptive immune response. This means that they are typically made to handle very specific pathogens that may be encountered in the body. Before they are released into circulation, both must undergo negative selection, which makes sure that they do not respond to natural peptides that they encounter in the body. Failure of this step to take place can result in autoimmune diseases.

Many of the modulations of the immune response are controlled by helper T cells. In order to change the type of antibody secreted by a B cell, helper T cells need to interact with them via a number of cytokines. The types of cytokines secreted by helper T cells will tell the B cells which antibodies to start secreting.

The type of blood a person has not only tells us which antibodies they create, but also which blood type can be given in the event of a transfusion. A person with type A blood has A antigens on his red blood cells. As a result, the person does not make A antibodies; these would bind to the A antigens and initiate an autoimmune response.

Because the person does not make the B antigen, there are B antibodies in the body. This means that the person cannot be given type B blood. B type blood cells would be targeted by the antibodies present in the body, causing an autoimmune reaction against the foreign blood. Since type O blood does not have any surface antigens, this blood type can be given to anybody. No antibodies will react with type O blood.

B cells play numerous integral roles in the immune response against foreign pathogens (viruses, bacteria, and fungi), including forming transient microenvironments called germinal centers, where they produce long-lived plasma cells that are high affinity for specific antigen and memory B cells. They also serve as antigen-presenting cells and producers of cytokines and chemokines; However, B cells are not able to produce extracellular traps, which primarily are composed of DNA and work to trap pathogens. Neutrophils produce extracellular traps.

Naive B cells (and most other immune cell subtypes) need more than one signal to become activated. They normally need B cell receptor signaling (signal 1), costimulation by other receptors (signal 2), and cytokines/chemokines (signal 3). This system is necessary in order to prevent aberrant activation of lymphocytes (safeguard against autoimmunity).

In regards to the other statements, there are numerous autoreactive B cells at any given time due to the stochastic nature of VDJ recombination and germinal center reactions. Therefore, tolerance mechanisms and checkpoints are incredibly important to keep these cells in check; central and peripheral tolerance are equally important. Self-nuclear reactive B cells and T cells are both necessary and critical in autoimmune pathogenesis. Female sex hormones are definitely believed to contribute greatly to autoimmune disease pathogenesis (e.g. estrogen). Over 75% of autoimmune patients are women.

The left atrium receives blood from the pulmonary veins, which carry blood that was freshly oxygenated from the lungs to the heart. The partial pressure of oxygen is always highest soon after oxygenation, thus blood returning from the lungs would have a high partial pressure.

The superior and inferior vena cavae return deoxygenated blood from the body to the heart, and would have very low oxygen partial pressures. The right atrium receives this deoxygenated blood from the vena cavae and transfers it to the right ventricle. From the ventricle, the deoxygenated blood is transported to the lungs via the pulmonary arteries. It only becomes oxygenated again after reaching the lungs, and then returns to the heart through the pulmonary veins.

We know that systemic arteries carry oxygenated blood away from the heart and that these vessels pass through tissues, allowing oxygen to diffuse into the tissues and carbon dioxide to diffuse out into the bloodstream. We also know that veins carry blood back to the heart, which by this time is oxygen-poor due to its gas exchange with the tissues of the body. The partial pressure of oxygen in veins must be lower than it is in arteries, since the veins carry deoxygenated blood.

The remaining statements regarding gas exchange are true.